John,
Please see picture for Electric Hand vacuum connected to the manifold. Hope this helps a little.

Thanks Bill. I saw your photo, then compared it with a salvage intake manifold I have. The salvage manifold has the remains of a copper vacuum tube sticking out of an identical hole. The location isn't exactly what the manual shows, but that's clearly what it was for. That clears that up!

The whole vacuum clutch/electric hand mechanism look very complex and problem - prone. No wonder Hudson eventually dropped the system. A floor shifter isn't all that bad.

Actually, your initial assumption is correct. there was a one-way ball valve fitting in the "underneath hole" to allow pooled fuel to drain out when the engine is not running. Engine vacuum held the ball up when running. Unfortunately sometimes this ball stuck open affecting the idle mixture, so most were taken out. Hope this helps.

Thanks, Geoff, that does help. I assume the fix is to replace the one way ball valve with a bolt?

Hello Geoff, I went to my salvage intake manifold and found that, as you stated, it is a one way ball valve. My ball valve is frozen by rust, but that's clearly the function. Underneath the ball valve is a fitting for a copper drain tube. Someone in the past solve any idling problem by cutting the copper tube, then pinching it closed. Here is a photo, for those interested in Hudson esoterica

I had thought that the ball valve was introduced in the 1937 model year, not the 1936. But, a previous owner might have replaced the '36 manifold with a '37.

When I purchased my 1937, fifty years ago, the ball valve had been replaced with a bolt. But late I found a ball valve on a junked '37, and -- thinking it was a good idea -- installed it. I have had no problems, and -- when the engine floods -- it does provide a way to drain the manifold of gasoline.

I used to think that a good way to check for correct operation of the ball, was to hold my finger over the bottom opening of the copper drain line with the engine running. If one felt vacuum, it would mean that the ball was rusted in the open position. However, as I think about it, wouldn't one's finger create a new closed "valve" further down the line? If so, the ball would no longer be held by the vacuum in the manifold, it would be your finger that now held the vacuum, and the ball valve itself would open. Thus, sensing vacuum in your finger would NOT indicate the ball was rusted open.